A copper clad polyimide substrate is used as flexible printed board, TAB material or CSP material; however, along with the miniaturization of the hardware and the speeding up of signal transfer rate, micro processing such as high density micro wiring or micro via becomes necessary, more requiring materials having a higher adhesion strength of the metal film.
In the prior art, in order to obtain a copper clad polyimide substrate having a higher adhesion strength, a process in which the polyimide surface is submitted to a dry pretreatment such as ion bombard, corona discharge before deposition a primer metal such as nickel or chromium by a spatter and electroless plating and electrolytic plating are executed thereon to form a metal film has been adopted.
However, this process requires an expensive equipment for performing pretreatment or spattering in the vacuum, lowers the production volume, and increases the cost, and it is difficult to say this process is industrially advantageous.
On the other hand, in case of producing a copper clad polyimide by imparting catalyst and executing electroless plating or electrolytic plating, without dry pretreatment nor spatter treatment, an expensive equipment is unnecessary, but there is a problem that the adhesion strength between metal and polyimide is so low that it is practically unusable.
As a means for forming a metal layer on the laminates surface, there is a process using palladium chloride catalyst taking stannous chloride as a reductant, and recently, a process for absorbing palladium catalyst by the reaction between a zinc oxide film and palladium oxide and reducing by a reductant, or a process for reducing metal(Pd) ions, by irradiating zinc oxide (photo semiconductor) with light, in order to form a metal layer on the surface of glass or ceramics, are reported in “Electronics Packaging Technology (VOL. 11, No. 6, P32, 1995)”; however, this process could not be applied to organic materials, because it is restricted to inorganic materials such as glass, ceramics on which zinc oxide thin film can be formed easily and adheres strongly.
Moreover, a process for alkali hydrolyzing the surface of a polyimide film to make polyamide acid, then absorbing copper or palladium ion by reacting with copper sulfate or palladium chloride and, thereafter, irradiating with ultraviolet of a low pressure mercury lamp using sodium formate as a reductant (The 13th Electronics Packaging Society Lecture Book P183, 1999) has been reported; however, it takes extremely long for forming catalyst nuclei by ultraviolet irradiation, and moreover, there was a problem that the decomposition of the reductant generates NaOH, which is alkaline and deteriorates the polyimide film.
Furthermore, as any of the aforementioned processes is a process for forming a metal layer only on the surface of laminates, it is impossible to obtain a so-called anchor effect where the metal layer penetrates into the laminates.
There, it has been proposed a process for forming a coating by melting a salt of rear metal on the surface of an object to be plated before reducing with a reducing gas such as hydrogen, CO, H2S (the Japanese Patent No. 1993-61296) or a process for combining a metal compound reduced only by contact with it and a metal compound that can be reduced directly by a reductant (the Japanese Patent Laid-Open No.1993-306469).
However, the process described in the Japanese Patent No. 1993-61296 provokes problems of the safety such as explosion and toxicity of reducing gas, while the process described in the Japanese Patent Laid-Open No. 1993-306469 has provoked loss of resin characteristics (strength, insulation and so on) because an addition amount of metal compound is necessary so large as about 200 weight parts per 100 weight parts of resin, and problems of insulation because not completely reduced metal compound remains in the resin, inducing easily metal ion migration and so on.
The present invention intends to provides laminates for electronic components of an extremely high adhesion strength with metal layers, without using an expensive equipment and of high insulating properties, without impairing characteristics inherent in the substrate, a cheap process for production of the laminates for electric components, and a polyimide resin precursor solution for using for the production of the same.